* {
    padding: 0;
    margin: 0;
}

header {
    height: 100px;
    border: 5px groove;
    margin-top: 25px;
    background-color: #ddd;
}

header h1 {
    margin: 20px 0 20px 0;
    text-align: center;
}

.theme_button {
    float: right;
    margin: 38px 20px;
    cursor: pointer;
}

.left_box {
    text-align: center;
    position: absolute;
    border-right: 5px groove;
    line-height: 50px;
    background-color: #ddd
}

.right_box {
    position: absolute;
    right: 0;
}

.middle_box {
    background: #fff;
    position: relative;
    left: 203px;
    margin-right: 203px;
}

.media {
    margin: 0;
    padding: 0;
}

footer {
    border-style: groove;
    text-align: center;
    background-color: #ddd;
}

.left_box,
.right_box,
.middle_box {
    height: 740px;
}

.container {
    width: 100%;
    height: 100%;
}
        
iframe {
    width: 99%;
    height: 737px;
}

.new1,
.new2,
.new3,
.new4 {
    float: left;
}

li {
    padding: 10px;
    margin-right: 5px;
    display: inline-block;
    /* 解决图片或文字不能左右排布的问题 */
}

div ul li p {
    color: red;
}

ul {
    float: left;
}

:target {
    display: block;
    background-color: aliceblue;
    position: relative;
    margin-right: 203px;
    height: 490px;
}

iframe {
    display: block;
    background-color: aliceblue;
}

div aside nav a {
    /* 所有超链接的字体颜色 */
    color: black;
    text-decoration: none;
}

div aside nav a:hover {
    /* 鼠标放上去时改变的颜色 */
    color: aqua;
    text-decoration: none;
}

div aside nav a:active {
    /* 鼠标点击时改变的颜色 */
    color: red;
}

nav {
    width: 200px;
}

.common {
    display: inline-block;
}

.selected{
    border: 1px solid #ddd;
}